A single metal atom stabilized on two dimensional materials (such as graphene and h-BN) exhibits extraordinary activity in the oxidation of CO. The oxidation of CO by molecular O2 on a single cobalt atom embedded in a hexagonal boron nitride monolayer (h-BN) is investigated using first-principles calculations with dispersion-correction. It is found that the single Co atom prefers to reside in a boron vacancy and possesses great stability. There are three mechanisms for CO oxidation: the traditional Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) mechanisms and the termolecular Eley-Rideal (TER) mechanism proposed recently. Given the relatively small reaction barriers of the rate-limiting steps for the ER, LH and TER mechanisms (0.59, 0.55 and 0.41 eV, respectively), all three mechanisms are able to occur at low temperature. The current study may provide useful clues to develop low cost single atom catalysts.

A three-dimensional (3D) lamellar SnO2 is grown on carbon cloth (CC) substrate (donated as 3D lamellar SnO2/CC) through hydrothermal reactions and subsequent thermal treatments. The resulting 3D lamellar SnO2/CC can be directly used as electrode of supercapacitors with no need for addition of either binder or conductive species, and achieve a specific capacitance as high as 247 F g -1 at a current density of 1 A g -1 within a potential window ranging from -0.6 to 0.3 V because of the unique porous structure accessible to electrolyte ions. In order to match the capacitive behaviors of 3D lamellar SnO2/CC in the two-electrode systems, reduced graphene oxide/carbon cloth (rGO/CC) is prepared by starting from GO. The rGO/CC and 3D lamellar SnO2/CC are respectively used as positive and negative electrode to assemble asymmetric supercapacitor. The device exhibits not only an excellent cycle stability (76.9 % after 10000 cycles at 3 A g -1 ), but also high energy density of 22.8 Wh kg -1 at the power density of 850 W kg -1 under a cell voltage of 1.7 V. Moreover, the as-fabricated supercapacitor has green and environmentally friendly features because aqueous neutral electrolyte is employed in it.

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